1. Field of the Invention
This invention relates generally to microwave transmit/receive (T/R) modules used in connection with an active aperture of a phased array radar system and more particularly to the method of fabricating T/R module packages utilizing laminated layers of low temperature co-fired ceramic (LTCC) material.
2. Description of Related Art
Phased array radars utilizing electronically scanned antenna arrays, also referred to as active apertures, require many individually controllable T/R modules which are arranged in an array. The T/R modules are connected to frontally located radiator elements which collectively generate a transmitted radar beam. The beam is normally energized, shaped and directed in azimuth and elevation under electronic control of the signals applied to the individual radiators.
Present state of the art T/R module packages include a structure in the form of a multi-cavity, multi-layer substrate comprised of high temperature co-fired ceramic (HTCC) layers including, for example, black alumina ceramics and tungsten. The ceramic layers have outer surfaces including metallization patterns of ground planes and conductors as well as feedthroughs or vertical vias formed therein for providing three dimensional routing of both RF and DC signals. Active circuit components comprised of integrated circuit chips are located in the various cavities of the substrate which implement suitable control and generating functions of RF signals to and from respective antenna elements. One such T/R module is shown and described in U.S. Pat. No. 6,114,986 entitled “Dual Channel Microwave Transmit/Receive Module for an Active Aperture of a Radar System”, issued to John W. Cassen et al. on Sep. 5, 2000, the details of which are incorporated herein by reference.
In the Cassen et al. patent, two discrete transmit/receive (T/R) channels are implemented in a single common T/R module package having the capability of providing combined functions, control and power conditioning while utilizing a single multi-cavity, multi-layer substrate comprised of high temperature co-fired ceramic (HTCC) layers.
Although packages for active and passive electronic components fabricated from multiple layers of low temperature co-fired ceramic (LTCC) tape are known in the prior art, the conventional method of fabricating these LTCC packages has been found to be adequate only for fabricating multi-layer substrates with a small number, typically 5-10 layers of tape. This method, however, has been found to be completely inadequate for fabricating highly complex packages of 20 or more layers of tape and having multiple cavities with different floor thicknesses, through-holes, and an integrated ring frame in the package as required, for example, by an LTCC T/R module utilized in a radar system.